The research activity of the group is focused on the theory and simulation of plasma-engine systems, and the different plasma propulsion concepts. For each type of engine considered, we first study in detail the different physical phenomena which govern the generation and acceleration of the plasma, and the interaction of the plasma with the elements of the engine (walls, magnetic fields, rf waves, etc.). This understanding allows us to develop appropriate mathematical models and simulation codes that can explain the coupled behavior of the different phenomena and the influence of each control and design parameter on the engine performance.
National R+D plans, EOARD (European Office of Aerospace Research & Development), ESA and the 7th Framework Programme are or have been the main financial sources for our research.
Hall Effect Thrusters
The core of the research carried out in the last decade has been dedicated to Hall Effect Thrusters, a mature technology which has already reached a flying status in both scientific and commercial satellites. Some of the most relevant results obtained by us are:
- The development of the first (partially) two-dimensional fluid model code of the plasma in the chamber and the near plume.
- Detailed models of the plasma-wall interaction process, covering secondary electron emmision, partial thermalization and wall erosion).
- Second and subsequent versions of the HPHall hybrid code, originally created in the Space Propulsion Laboratory (SPL) of the MIT. It is an axilsymmetric code that treats ions and neutrals with Particle-in-cell (PIC) methods, and employs an anisotropic fluid model to describe electrons. This code is the main reference in Hall Effect Thrusters simulation.
- Double stage engine models, with intermediate electrodes.
Among the collaborations with external institutions stand out the joint developments with MIT, the simulation/experiment comparison with Princeton Plasma Phyisics Laboratory (PPPL), the chamber wall erosion studies together with Inasmet, the double stage engine designs with Alta/Centrospazio(Italy), and the oscillation studies with the Institute of Plasma Physics and Laser Microfusion of Varsaw.
Helicon Thrusters and Magnetic Nozzles
In 2008 a new research line on Helicon Thrusters was opened, as a part of an European project for the design and development of a mini-helicon thruster. The ongoing research efforts are dedicated to understand:
- The plasma internal dynamics in the chamber, which consists of the helicon rf-wave energy absorption, ionization and plasma heating, plasma flow, and wall losses.
- Plasma acceleration in the outer magnetic nozzle, and the magnetic detachment thereafter. Magnetic nozzles consist on a convergent-divergent magnetic field that guides, expands and accelerates a plasma jet. They are currently being proposed as an efficient acceleration device for a number of space electric propulsion systems. They allow continuous thrust and specific impulse control, and avoid material contact with the hot plasma. These studies are of interest as well for a number of other engine concepts, such as VASIMR, and the Applied Field MagnetoPlasmaDynamic (AF-MPD) Truster. Also, they find application in other fields such as in advance manufacturing techniques with particle beams.
- Discontinuity formation (non-neutral double layers) inside the plasma jet under certain conditions and their effect on the propulsive performances.
Specifically, research on magnetic nozzles has led to the elaboration of a simulation code of associated the two-dimensional plasma flow, which has been baptized DiMagNo 2D. This code, based on the method of characteristics to integrate the supersonic jet in the diverging part of the nozzle, is fast and possesses a high accuracy, and constitutes the first code of its kind dedicated to the simulation of magnetic nozzles.
Guide magnetic field employed by DiMagNo 2D for plasma flow simulation in a magnetic nozzle.
Currently, one of the most active research lines in the group is the plasma detachment from the guide magnetic field downstream, once the plasma has been accelerated.
Other Research Lines
In 2009 the development of a hybrid code for plasma analysis for the Divergent Cusped Field Thruster (DCFT) was started together with SPL-MIT.
In the past, relevant research has been carried out on electrodynamic bare tethers for electric generation, propulsion, or satellite deorbiting. The interaction of plasma contactors with the ionosphere was also investigated, with applications to tether ends and spcecraft charge-control. Recently and in cooperation with the Space Dynamics Group of UPM LINK research was started on active debris removal from LEO and GEO by using Reversed Electric Propulsion and, eventually, bare tethers.
Finally, as a by-product of these research activities, a number of different studies were performed on plasma instabilities and surface interaction with magnetized plasmas, of application in related fields (plasma fusion, surface treatment, ionosphere-spacecraft interaction, ...).